Regioselective hydroxylation of isoflavones by Streptomyces avermitilis MA-4680

Screening of bacterial whole cells was performed for regioselective hydroxylation of daidzein and genistein. Among the strains examined, Streptomyces avermitilis MA-4680 showed high ortho-dihydroxylation activity to produce 3′,4′,7-trihydroxyisoflavone and 3′,4′,5,7-tetrahydroxyisoflavone from daidzein (4′,7-dihydroxyisoflavone) and genistein (4′,5,7-trihydroxyisoflavone), respectively. Using 100 mg cells (wet wt.) and 1% (v/v) Triton X100 in 1 ml of total reaction volume, where 100 μl of the substrate solution (0.5 mM in 10% (v/v) mixed solvent of DMSO:MeOH = 3:7) was added to 900 μl of potassium phosphate buffer (100 mM, pH 7.2), a 16% molar conversion yield of 3′,4′,7-trihydroxyisoflavone was obtained from 0.5 mM daidzein after 24 h of reaction time at 28 °C and 200 rpm. Ketoconazole significantly (ca. 90%) inhibited the ortho-hydroxylation activity of daidzein, suggesting that cytochrome P450 enzymes putatively play roles in regiospecific daidzein hydroxylation. The analysis of the reaction products was determined by gas chromatography/mass spectrometry (GC/MS) and 1H NMR.